1. Field of the Invention
This invention relates to apparatus for transferring signals between bodies undergoing relative rotation with respect to each other and, more particulary, to non-contacting optical couplers having the capability of transferring light signals.
2. Description of the Related Art
Mechanical couplers for transferring electrical current from a rotating body to a non-rotating body are well known in the art. Typically, a conducting ring on one body is contacted by one or more conducting brushes on the other body. Electric current flows from one body through the ring to the brush and then to the other body. This mechanical arrangement is subject to wear and creates electrical noise which may obscure the signals being transmitted. Mechanical couplers are often limited by their limited bandwidths and useful life expectancies. Optical couplers, on the other hand, may be composed of non-contacting mechanisms and are subject to virtually none of the bandwidth limits inherent in mechanical couplers.
Existing optical coupler mechanisms are limited in at least one of the following ways:
a. Low efficiency caused by multiple optical reflections and multiple boundaries of the optical coupler interface. PA1 b. Signal intensity modulation from rotary motion (the change of relative position between transmitters and receivers). PA1 c. Inability to support multiple numbers of rings. PA1 d. Poor signal noise ratio which results in the device being unacceptable for analog signal linkage. PA1 1. Hard vacuum can be realized. Troublesome condensation, particles such as dust, and reactive gas cannot enter the unit. PA1 2. The coupler bearing is the only hard moving part. No drive gear or belt is required. PA1 3. By nature of the coupling mechanism, there is no backlash to cause alignment problems. PA1 4. The relatively bulky transmitters and receivers can be freely spaced on designated mounting areas without additional mounting parts. This can translate to significant reductions in size and cost.
One example of optical couplers in the prior art is disclosed in patents 4,027,905 and 4,109,997 of Myren L. Iverson. The optical couplers of that patented arrangement have two light-carrying members, one attached to a rotating body and one attached to a stationary body. The light carrying members are bundles of optical fibers which are placed end to end coaxially with the axis of rotation. Light introduced into one bundle travels to the opposite end where it couples across a small gap into the second bundle. Since a gap exists between bundle ends, no physical contact is made. Multichannel bundles may be used where the channels of the coupled ends are each formed into concentric circles separated by opaque material. If discrete signal channels are to be incorporated in the bundles, this construction presents severe alignment requirements. Moreover, signal losses are inherent in this design configuration.
Other variations of optical couplers which are known in the art incorporate a series of fiber optic channels concentrically placed about a waveguide for the transfer of both light signals and microwaves from one body to the other. Still others utilize a de-rotating prism arranged to rotate at one-half the relative rotational speed between the two bodies. The de-rotating prism, arranged in this fashion, enables collimated light from a fixed light source on one body to be transmitted onto a fixed light detector on the other body. Still another variation uses concentric annular mirrors within a toroid which has a transparent circumferential window. Light signals from one body are projected through the circumferential window and into the toroid where they reflect back until they strike an angled mirror and are deflected out of the toroid. The toroid is attached to one body, and the light projecting means is attached to the other body. All of these designs incorporate complex structural configurations which are difficult and costly to fabricate with the mechanical precision required for effective coupling of signals between optical fibers. In addition, some of these designs are inherently lossy in the transmission of the coupled signals.
The design of the present invention minimizes or eliminates the problems outlined above. Since only a single reflection is necessary between transmitters and receivers, reflectivity may be consistently held above 99.9%. Other advantages of the present invention are:
It is the combination of these advantages that make this invention producible, practical and usable.